- 266 - The CEA also presents operating provisions for alerting to the imminence of a flood: monitoring of the river Rhone (level, flow rate, height, flood risks) via the "Vigicrues" web site; the alert given by Météo France if extreme weather conditions are forecast. The situation of the site nevertheless reveals weaknesses in the supervision-office building (BCB) and the pumping station which suggest that beyond the 38 m NGF level there is a flood risk for the reactor building basements, the reactor pit, the SG building and the handling building, but it would be limited to water infiltrations from the auxiliary building penetrations. Conformity of the facilities with the current frame of reference The CEA indicates that the main measures for guaranteeing the conformity of the facility are: verification of lift pump operation by performing two-weekly tests; verification, as part of the CSAs, of the condition of the roofs and storm water downpipes. The CEA also envisages scheduling periodic inspection of the storm water drainage systems. Consequently, the CEA considers that for the Phénix facility the main flood risks come from heavy rainfall and flooding of the nearby river Rhone. The risk of a cliff-edge effect exists in the event of a sodium-water reaction induced by the displacement of the secondary sodium storage tanks which are simply placed on skids in the basement of the handling and SG building. Evaluation of the safety margins The CEA has presented the effects of a rise in the level of the river Rhone, particularly beyond the CMS, then beyond the elevation of the facility platform (38.70 m NGF), leading to flooding of the buildings. The licensee points out however that overspills above the left-bank embankment opposite the facility would limit the increase in water level. It therefore considers that to reach the platform it would require flood flows much higher than those associated with the CMS. The licensee rules out any significant risk resulting from an extreme rise in the water table, on account of the means of protection implemented in the buildings containing essential equipment and the absence of cliffedge effects in the event of infiltrations into the auxiliary buildings. The CEA indicates that rainfall exceeding the capacity of the drainage system could lead to a flash flood on the facility platform inducing a risk of flooding the buildings. The licensee proposes a complementary study in this respect to evaluate the ability of the plant's storm water drainage system to evacuate the water from very intense rainfall episodes. Measures envisaged to reinforce the robustness of the facilities to the flood risk Considering all these elements, CEA envisages: Remedying the facility's weak spots by: o installing isolating devices on the overflow lines linking the main diesel generator set cooling system tanks to the tank situated in the BCB basement; o evaluating the resistance of the fire barrier penetrations between the basements of the auxiliary, handling, SG and reactor buildings to a height of water, and study their reinforcement if necessary; Favour the overflow of the water towards the IPE (area adjacent to the SG building containing the hall of shut down turbines) by means of openings made in the connection gallery between the BCB and the auxiliary building; Procure means for limiting water ingress (inflatable tubes, etc.) and establish a procedure for preparing mobile pumping means in case of an announced rise in water level or heavy rainfall; Study the dimensioning of the plant storm water drainage system with respect to its capacity to evacuate the water from very intense rainfall episodes, exceeding those already encountered; Perform periodic inspections of the plant storm water drainage systems; Render watertight an opening giving access to a sodium tank situated at the low point of the reactor building.
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